1 files changed, 110 insertions, 0 deletions
diff --git a/source_undo.lua b/source_undo.lua
new file mode 100644
index 0000000..0aa6755
--- /dev/null
+++ b/source_undo.lua
@@ -0,0 +1,110 @@
+-- undo/redo by managing the sequence of events in the current session
+-- based on https://github.com/akkartik/mu1/blob/master/edit/012-editor-undo.mu
+
+-- Incredibly inefficient; we make a copy of lines on every single keystroke.
+-- The hope here is that we're either editing small files or just reading large files.
+-- TODO: highlight stuff inserted by any undo/redo operation
+-- TODO: coalesce multiple similar operations
+
+function record_undo_event(State, data)
+  State.history[State.next_history] = data
+  State.next_history = State.next_history+1
+  for i=State.next_history,#State.history do
+    State.history[i] = nil
+  end
+end
+
+function undo_event(State)
+  if State.next_history > 1 then
+--?     print('moving to history', State.next_history-1)
+    State.next_history = State.next_history-1
+    local result = State.history[State.next_history]
+    return result
+  end
+end
+
+function redo_event(State)
+  if State.next_history <= #State.history then
+--?     print('restoring history', State.next_history+1)
+    local result = State.history[State.next_history]
+    State.next_history = State.next_history+1
+    return result
+  end
+end
+
+-- Copy all relevant global state.
+-- Make copies of objects; the rest of the app may mutate them in place, but undo requires immutable histories.
+function snapshot(State, s,e)
+  -- Snapshot everything by default, but subset if requested.
+  assert(s)
+  if e == nil then
+    e = s
+  end
+  assert(#State.lines > 0)
+  if s < 1 then s = 1 end
+  if s > #State.lines then s = #State.lines end
+  if e < 1 then e = 1 end
+  if e > #State.lines then e = #State.lines end
+  -- compare with App.initialize_globals
+  local event = {
+    screen_top=deepcopy(State.screen_top1),
+    selection=deepcopy(State.selection1),
+    cursor=deepcopy(State.cursor1),
+    lines={},
+    start_line=s,
+    end_line=e,
+    -- no filename; undo history is cleared when filename changes
+  }
+  -- deep copy lines without cached stuff like text fragments
+  for i=s,e do
+    local line = State.lines[i]
+    table.insert(event.lines, {data=line.data, dataB=line.dataB})
+  end
+  return event
+end
+
+function patch(lines, from, to)
+--?   if #from.lines == 1 and #to.lines == 1 then
+--?     assert(from.start_line == from.end_line)
+--?     assert(to.start_line == to.end_line)
+--?     assert(from.start_line == to.start_line)
+--?     lines[from.start_line] = to.lines[1]
+--?     return
+--?   end
+  assert(from.start_line == to.start_line)
+  for i=from.end_line,from.start_line,-1 do
+    table.remove(lines, i)
+  end
+  assert(#to.lines == to.end_line-to.start_line+1)
+  for i=1,#to.lines do
+    table.insert(lines, to.start_line+i-1, to.lines[i])
+  end
+end
+
+function patch_placeholders(line_cache, from, to)
+  assert(from.start_line == to.start_line)
+  for i=from.end_line,from.start_line,-1 do
+    table.remove(line_cache, i)
+  end
+  assert(#to.lines == to.end_line-to.start_line+1)
+  for i=1,#to.lines do
+    table.insert(line_cache, to.start_line+i-1, {})
+  end
+end
+
+-- https://stackoverflow.com/questions/640642/how-do-you-copy-a-lua-table-by-value/26367080#26367080
+function deepcopy(obj, seen)
+  if type(obj) ~= 'table' then return obj end
+  if seen and seen[obj] then return seen[obj] end
+  local s = seen or {}
+  local result = setmetatable({}, getmetatable(obj))
+  s[obj] = result
+  for k,v in pairs(obj) do
+    result[deepcopy(k, s)] = deepcopy(v, s)
+  end
+  return result
+end
+
+function minmax(a, b)
+  return math.min(a,b), math.max(a,b)
+end